The Western Star

CINDY DAY: Walking around with your head in the clouds

This cloud looks as light as a feather! Faye Murphy spotted the cirrus cloud high above the ground near Pugwash, N.S. - Contributed

Yesterday I answered a young boy’s question about clouds. I thought I would elaborate a little.
The atmosphere is a dynamic system, and the local conditions of turbulence, uplift and other parameters give rise to many types of clouds. The main factors are temperature and air pressure. Let’s start at the top and work our way down:
Clouds form because the air cools enough to condense the water out of them into droplets.
In good weather (high air pressure), water vapour can rise all the way into the cold region of the troposphere (above 6,000 metres) before it forms cirrus clouds. These cirrus clouds are made of ice crystals and often look like feathers.
Mid-level clouds, known as alto clouds, form when a large mass of air is lifted and then condensed. This usually happens when a frontal system approaches. Mid-level clouds often bring steady rain or snow.
Low-level clouds or cumulus clouds, typically form when warm air rises and reaches a level of relatively cool air, where the moisture in the air condenses. This usually happens through convection, when a parcel of air is warmer than the surrounding air. The height at which the cloud starts to form is the cloud base and that point depends on the amount of moisture available. Humid air will generally result in a lower cloud base. Around here, the base of the cumulus cloud reaches about 2,400 metres above the ground. In arid and mountainous areas, the cloud base can be as high as 6,000 metres.
One question kids often ask is, “why are clouds white?” They appear white because they reflect light from the sun. Gray clouds become so filled with water that they don’t reflect light.
Finally, a word about fog. Did you know that fog is a cloud? It’s a stratus-type of cloud that appears very close to the ground.
Keep looking up and if you happen to spot an interesting looking cloud, take a photo and send it along to weathermail@weatherbyday.ca